Tsunami Disaster Countermeasures Based on the Lessons Learned from

the Great East Japan Earthquake

March 16, 2015

Masahiko IsobeVice President, Kochi University of Technology

President, Japan Society of Civil Engineers

Runup height of the Great East Japan Earthquake Tsunami was extraordinary higher than the recurrent tsunamis in the past century.

[from Joint Survey Group for Great East Japan Earthquake Tsunami （ http://www.coastal.jp/ttjt/, April 30, 2011 version)]1

Tohoku (2011)Meiji (1896) Showa (1933)

comparable tsunami: Jogan (869)

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Heavy damage was caused by the tsunami.

Taro Coast in Iwate Prefecture

Even though being overtopped, structural protection facilities effected to reduce damage in the city behind.

［ Expert Panel on Countermeasures for Earthquake and Tsunami based on Experience of Off Tohoku Earthquake Tsunami, Central Disaster Prevention Council ］

Kamaishi City

Breakwater

Runup height of tsunami was lower in the city behind the breakwater.

24.63m

8.38m

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We apply “multiple protection” that combines resilient structural measures and region-wide non-structural measures to minimize loss of lives and assets from all possible hazards.

Tsunami height after 1896 Meiji-Sanriku earthquake

Tsunami height after 1933 Sanriku earthquake

Tsunami height after 1960 Chile Earthquake

Tsunami height caused by the 2011 Great East Japan Earthquake

Level 2 ＜ Maximum Level Tsunami ＞- For establishing integrated disaster countermeasures

focused on the evacuation of residents

Level 1＜ Comparatively Frequent Tsunami＞- For designing the heights of coastal levees (tsunamis

occurring once every several decades to once every one hundred years plus several decades )

While preventing inundation from Comparatively Frequent Tsunamis, we save lives and keep operational minimum required socioeconomic functions from Maximum Level Tsunamis.

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Restored coastal levee

　- Aim to prevent damage to human lives as much as possible against

a maximum level tsunami through “Multiple Protection” combining structural and non-structural measures such as land use regulations, the building code, and warning and evacuation procedures.

Fundamental strategy for tsunami disaster measures

- Reducing human and economic damage through disaster mitigation is fundamental for all levels of tsunami.

- Two levels of external forces are set.

　- Aim to ensure the protection of human lives, assets and national

land (coastal line), etc. against a comparatively frequent tsunami (once every several decades to once every one hundred years plus several decades) by construction or improvement of the coastal protection facilities.

- Undertake the technical development and improvement of structures so that they are not easily broken even when the tsunami height exceeds the design level.

Comparatively frequent tsunami

Maximum level tsunami

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8Coastal levee

Land raising ofresidential area

Tsunami Evacuationbuilding

Tsunami Evacuationtower

Evacuation routeEvacuation site(high ground)

Estimated tsunami inundation zone

Tsunami priotection structure(multiple use structure)

Zones to be protected

Zones to be protected

Tsunami protectionstructure

(inland lock gate)

Designated tsunamiadaptation structure(existing road)

Tsunami Disaster Security Zone 　Hazard map + Evacuation.

Tsunami Disaster Special Security ZoneRooms of hospitals etc. above the estimated tsunami water level

Tsunami Disaster Special Security Zone designated by municipalitiesRooms of residence above the estimated tsunami water level

Tsunami Evacuationbuilding

Tsunami Evacuationtower

Tsunami-resilient community (Multiple protection)

Sandy beach